Abstract: Objective To develop a liquid chromatography-tandem mass spectrometry （LC-MS/MS） method for the simultaneous determination of desloratadine and its metabolite 3-OH desloratadine in human plasma. Methods 24 healthy male volunteers received a single oral dose of 5 mg desloratadine tablets in a randomized crossover bioequivalence study with two preparations of tablets. Serial plasma samples were taken and analyzed by the LC-MS/MS method. The pharmacokinetic parameters of the two preparations were calculated and compared statistically to evaluate their bioequivalence using Winnonlin 6.3. Results The calibration curves of desloratadine and 3-OH desloratadine were both linear over the concentration range of 0.050-6.0 ng/mL, with intra-batch and inter-batch relative standard deviations less than 15%. The 90% confidence intervals (CIs) of peak concentration （C_max），area under the curve （AUC）_0-t and AUC_0-∞ of desloratadine and 3-OH desloratadine all resided within the bioequivalence limit 80%-125%. No significant difference in peak time (t_max) was demonstrated between the two preparations. Conclusion The LC-MS/MS method can be used for simultaneous determination of desloratadine and 3-OH desloratadine in human plasma, which has been successfully applied to a bioequivalence study.